Unify 2 versions of "sometimes not all components are available"

[rami3l]

Before 983e9fa this was actually coherent (cc @djc).

IMHO this is more of a note: kind of message (but made probably before the logging convention was fully established), otherwise it doesn't make too much sense to put a newline before it?

rustup/src/dist/mod.rs

Lines 87 to 93 in de2b979

	if toolchain.starts_with("nightly") {
	let _ = write!(
	buf,
	"\
	Sometimes not all components are available in any given nightly.
	If you don't need these components, you could try a minimal installation with:

rustup/src/errors.rs

Lines 205 to 210 in de2b979

	if toolchain.starts_with("nightly") {
	let _ = write!(
	buf,
	"(sometimes not all components are available in any given nightly)"
	);
	}

It'd be better if we can think of an appropriate way to unify those.

[djc]

Probably okay to turn this into note:, I think I mainly changed it to get rid of the capitalization.

[enthropy7]

Would it make sense to extract the nightly “components may be missing” text into a single helper pub(crate) and reuse it in both call sites? That would avoid having two slightly different versions and make future wording changes a one-liner.